But if you look under "commits" you might get the impression that it's 0.8.13.
Author Commit Message Labels Comments Approvals Date
Coin Nas f87464e M Merged JeanLucPicard/nxt into master 2014-04-11
Jean-Luc Picard 401e1d8 M Finish 0.8.13 2014-04-01
Jean-Luc Picard ffa873b fixed to use a Map 2014-04-01
Jean-Luc Picard 17d6af9 0.8.13 changelog 2014-04-01
Jean-Luc Picard 7313903 prevent duplicate hash transactions in the unconfirmed transactions 2014-04-01
...
I really don't understand why. But there is not a greater version label than 0.8.11 in this repository:

and the files on it are exactly the same as version 0.8.11 of "JeanLucPicard / nxt", except for "List4GenesisBlock" file added. So, it doesn't help, it is not really NAS source code :-( , it means that they never did commit NAS specific code.
Version 0.8.13 was the first version of NXT that was packaged for download, as far as I can see, and it is the last one of 0.8.x:
https://nxtforum.org/nrs-releases/60/https://bitcointalk.org/index.php?topic=345619.0Is it casual that NAS first and only source code is also this version?
Comparing date of files between nas-0.8.13(N1) and nxt-0.8.13, it looks that the following 12 files has NAS specific code:
Constants.java
BlockchainProcessorImpl.java
TransactionProcessorImpl.java
DebugTrace.java
Account.java
DbVersion.java
Nxt.java
Asset.java
BlockDb.java
TransactionType.java
Attachment.java
VeryfyTrace.java